1. Field of the Invention
This invention relates generally to desalination, salt production, and water production. In particular, it relates to a process for converting a saltwater desalination reject stream into pure salt, where this desalination process can be via thermal process or via membrane process.
2. Description of Related Art
As is stated in U.S. patent application Ser. No. 12/345,856 filed on Dec. 30, 2008, herein incorporated by reference, for centuries, common salt has been produced by evaporative concentration of seawater or of another naturally occurring brine, typically by using open-air evaporation lagoons or thermal concentration equipment and processes. A number of modern industrial processes require salt of substantially high purity, such as a sodium chloride salt substantially free of undesirable chemical or taste components. Such high purity salt may be mined from some natural geological formations, and may also be obtained from other saline waters by concentration and treatment steps that remove the principal unwanted impurities present in a starting solution.
Potable, high-quality or pure water has also historically been produced, when fresh water is not available, from natural saline or brackish waters, originally by thermal processes such as freezing or distillation, and more recently by membrane processes such as reverse osmosis or membrane vapor permeation, and/or by hybrid membrane/thermal processes. When starting with a saline feed, all of these water production processes recover or purify only a fraction of the water present in the feed, and generally produce waste brine that is substantially more concentrated than the original feed stream.
One problem is that seawater and other natural saline waters contain many solutes and impurities, so the salt-enriched side streams of a pure water production process, i.e., the concentrated reject of a reverse osmosis water treatment, or the residue of a distillation process, include other solids that both limit flux or treatment rate and/or recovery of the water side and must be removed on the brine side if a high quality salt is desired. These dissolved solids can be corrosive and scale forming in the salt plant evaporators and crystallizers. Currently, chemicals are introduced on the brine side to prevent or reduce the scale formation. These chemicals are costly and reduce the salt purity.
Accordingly, a need exists for a non-chemical purification solution to reduce or prevent scale formation in the salt plant.